UC San Diego Library – Scripps Digital Collection

The sardine population along the Pacific Coast of North America is subject to large fluctuations in the survival of sardines from each season's spawning. This results in some very abundant year classes, some very sparse and some of intermediate strengths. The relative abundance of each year class can be measured in its second or third year when it is first taken in the commercial fishery but it is of material help to the industry and to the biologist to know the abundance of each year class as early as possible. The California Department of Fish and Game has attempted to measure such abundance by surveys along the coast in the late summer and fall months when a new year class of sardines is about six months old.

The first exploratory surveys were conducted in California and Mexican waters during the fall months of 1938, 1939 and 1940. These were discontinued because the correlation between the observed abundance of young fish on the nursery grounds and the subsequent abundance of these fish in the commercial catch was not in good agreement. This was due in part to lack of certain equipment, such as recording echo-sounders, which were not in general use at that time, and in part to an exceptional spawning in 1939 north of the area covered by the survey. This resulted in a serious underestimate of the abundance of the 1939 year class.

Since the earlier survey, the need for a knowledge of the strength of incoming age groups has become even greater. The older sardines, which acted as a buffer against wide fluctuations in the strength of individual year classes, are no longer on the fishing grounds. As a result the industry is dependent upon younger fish, and a weakened fishery now exists which yields a widely fluctuating harvest, varying as varies the abundance and distribution of young sardines one to three years old.

There have been many new developments since the earlier surveys that aid in collecting and compiling the data. The evaluation of the strength of year classes is now possible through the development of a method of age determination. The relative abundance of a year class can now be traced from its first appearance in the commercial catch until it is no longer taken in the fishery. During the surveys sardines of all age groups can be collected and their estimated abundance checked against similar estimates from the commercial catch.

The California Cooperative Sardine Research Program under the auspices of the Marine Research Committee is collecting data regarding concentrations of sardine eggs and larvae throughout the distribution of the sardine. This information about the location of sardine spawn is collected each season prior to the beginning of the young fish survey and the range of the survey can be established thereby. This should prevent omission from the survey of the nursery grounds to the north or south of the usual spawning area as occurred for a major part of the 1939 year class.

New tools are also most useful. The development of radar has been of great help in allowing the vessel to work closer inshore at night. It also makes it possible to define more accurately the locations where fish are found. The echo-sounder aids in finding schools which cannot be located visually.

Although the earlier surveys are not directly comparable with the later, some marked differences in the two time periods are evident. The most striking is the greater abundance of young sardines in all areas in 1938–40 than in 1950–51. Although this is most apparent in Central and Southern California it is also true for the Baja California region. There is no indication that lack of sardines in California waters in the later years has been compensated by an increase in abundance off Baja California.

The maximum surface temperatures where sardine schools were found are similar for both time intervals. The 1938, 1939 and 1940 surveys were extended farther south than the 1950 and 1951 cruises but sardines were not found at temperatures greater than 26.1° C. In the later surveys the highest temperature at which sardines were found was 25.7° C. The maximum surface temperature encountered on all cruises was 28.3° C. The later cruises recorded minimum temperatures as low as 10.4° C. but no sardines were located at temperatures below 11.4° C. The lowest temperature on the earlier cruises was 11.7° C.